1. Field of the Invention
The present invention generally relates to a jig which is adapted to be bonded to one of opposite surfaces of a contact lens material which has been machined, for holding the lens material while the other surface is machined. In particular, the invention is concerned with such a jig as described above, which is bonded to the contact lens material with high uniformity in bonding strength, thereby assuring enhanced accuracy with which the lens material is machined, and which permits accurate measurement of a front curve of a contact lens formed from the contact lens material while the material is bonded to the jig.
2. Discussion of Related Art
In a conventional method for producing a contact lens, a suitable lens material is fixed to a spindle which is rotatable about an axis, and one and the other of the opposite surfaces of the lens material are sequentially subjected to machining operations, such as cutting and grinding, and further to suitable treatments as needed. More specifically described, one of the opposite surfaces of the lens material, which gives a concave inner surface of the contact lens, is first subjected to the cutting and grinding operations and other treatments, and the other surface of the lens material, which gives a convex outer surface of the contact lens, is then subjected to similar machining operations and treatments, so that the opposite surfaces of the lens material respectively provide desirably shaped inner and outer surfaces of the contact lens.
In the above process of producing the contact lens, the above-indicated other surface of the lens material is machined while the above-indicated one surface, which has been machined to form the concave inner lens surface, is held by a suitable jig through which the lens material is attached to the spindle. Thus, the inner lens surface is protected during the machining operations on the other surface of the lens material.
The jig favorably used in the above process includes a protruding portion which has a top end having as its outer surface a convexedly curved surface that substantially follows the concave inner lens surface formed by machining the above-indicated one surface of the lens material. The jig is bonded at its convexedly curved, top end face to the concave lens surface so as to hold the lens material in position. In this case, an ultraviolet-curable (UV-curable) bonding agent or adhesive is particularly favorably used as a bonding agent for bonding the jig and the lens material together. The UV-curable bonding agent, which is interposed between the convex surface of the top end of the jig and the concave surface of the lens material, is irradiated from the outside with an ultraviolet radiation, and is thus cured. This permits the lens material to be freely removably bonded to the jig, without affecting the lens surface bonded to the jig, while suitably controlling the time when the curing of the bonding agent is initiated. Thus, the use of the above bonding agent ensures improved efficiency with which the contact lens material is machined.
In the conventional jig used as described above, a recess is formed on the rear side of the protruding portion opposite to the top end face (convexedly curved surface) to be bonded to the lens material, so that optical fibers are inserted into the recess which extends inwardly of the protruding portion, and the bonding agent is irradiated with ultraviolet radiation transmitted through the optical fibers. This arrangement meets a requirement for continuously processing the contact lens materials so as to form one contact lens after another. In this arrangement, however, a variation in the intensity of the ultraviolet radiation may arise at the top end face of the protruding portion which serves as the bonding surface, resulting in non-uniform or inconsistent curing of the bonding agent, and consequent variation in the bonding strength between the lens material and the jig. Consequently, the lens material may be distorted during a cutting operation, for example, resulting in reduced machining accuracy, or may even be removed from the jig in some cases.
In addition, the contact lens thus produced from the lens material is usually inspected in terms of its nominal specifications according to predetermined standards, by irradiating the convex outer surface of the lens, and detecting a light reflected by the convex outer surface so as to measure a radius of curvature, that is, a front curve of the outer lens surface. If this inspection is effected while the contact lens material is bonded to the jig, the light incident upon the outer lens surface may also be incident upon and reflected by the inner wall of the recess formed on the rear side of the jig, and the thus reflected light may cause a noise, which makes it difficult to measure the front curve of the lens surface with sufficiently high accuracy. Therefore, the above-described inspection for the contact lens is conventionally effected in a separate process step after the contact lens material which has been machined is removed from the jig, resulting in a considerable reduction in the production efficiency of the contact lenses.